The invention relates to an apparatus for manufacturing a glass stem, and more particularly, to an apparatus having a plurality of forming stations each of which has a universal stem mold including a mold block having a plurality of novel fillet-forming means therein. The fillet-forming means at one of the stations is different from the fillet-forming at at least one other station.
In the prior art, it is known to have a stem manufacturing apparatus comprising a plurality of forming stations. Two, three or even four stations are commonly utilized. In the process of forming glass stems for vacuum devices, a body of glass, a tubulation and a plurality of lead-in conductors (or leads) are positioned on a rotatable lower portion of a stem mold assembly, heated and subsequently pressed by a conventional upper portion of the stem mold assembly, when the glass reaches the proper temperature, to form the glass stem. The forming of pressing operation is frequently repeated, two, three or even four times on the same stem to insure that a proper leak-tight well-defined stem is produced. In one type of conventional stem manufacturing apparatus described hereinafter, four separate, pressing stations are utilized. Stations one and two are identical to each other, and stations three and four are also identical to each other but different from stations one and two. The upper stem mold assembly of each station, and particularly the mold blocks, which contact the molten glass, and locate and form the fillets of the stem, are expensive items to manufacture. Each mold block requires precision machining, and the drilling of long small diameter holes to tight tolerances with no taper to the holes. Because of this requirement, upper stem mold assemblies are not only expensive and difficult to make, but manufacturers are reluctant to change stem designs, for example to change either the inner lead diameter or length, the fillet shape, the location of a dummy fillet, or the number of leads or dummy fillets per stem because each change required the manufacturing of a different upper mold block.
The mold blocks, of course, have a finite life and it is necessary to replace them when failure occurs. Such failure is caused by hot glass which erodes the bridges between adjacent fillets and causes reentrant angles which results in cracked stems. Mold block failure also occurs because the hot nickel leads of the lead-in conductors wear the centering holes which orient the stem leads and cause the holes to become oblong causing bent pins and pin circle displacement.
The need thus exists for a simpler, cost effective apparatus for forming glass stems and in particular for an apparatus which utilizes a common mold block at each forming station but novel fillet-forming means to provide the station-to-station differences required to produce different types of stems or replace worn components at reasonable cost.